Writing instruments in which inks are penetrated into pen tips comprising a fibrous feed or a plastic feed as is the case with a marking pen, a felt-tip pen and a writing brush pen-have so far been used in many cases.
However, when a cap is taken away to leave a pen tip part to stand in the air for a long time, there involved is the problem in that the pen tip part is dried to cause inferior writing.
In the past, in writing instruments such as a marking pen, a ballpoint pen, a felt-tip pen and a writing brush pen which are excellent in a cap-off performance of inhibiting drying at the pen tips, higher fatty acid esters of polyglycerin were added to inks (Japanese Patent Publication S62-34352/1987); paraffin waxes which can be deposited on the surface of a pen tip to form a thin film were added to inks (Japanese Patent Publication H01-35028/1989); hexaglyceryl tristearate was added to inks (Japanese Patent Application Laid-Open No. H02-232277/1990); and lecithin was added to inks (Japanese Patent No. 2594457).
However, many of additives having a high vaporization-inhibiting effect have a low solubility (10% by weight or less) in ink solvents and has a problem in terms of this low solubility. In particular, the solubility in the vicinity of 0° C. is low (5% by weight or less), whereby there involved are the problems in that precipitations of the additives are produced in the inks while pens are stored at a low temperature or exposed repeatedly to low and high temperatures, thereby causing clogging in the ink passages to reduce the writing property or deteriorating the cap-off property with the passage of time. Thus, the effective vaporization-inhibiting effect is not yet achieved.
Accordingly, the present inventors have filed a patent application for writing instruments such as a marking pen, a felt-tip pen and a writing brush pen having an excellent cap-off performance in which a pen tip comprising a fibrous feed or a plastic feed is coated with a substance such as paraffin wax providing a cap-off property (PCT Publication WO2000/37265).
A substance such as paraffin wax providing a cap-off property has an excellent effect, but paraffin wax has a low critical surface tension, so that the ink is a little deteriorated in a wetting property with respect to the pen tip to cause the problem of reduction in the ink discharge amount. Further, there involved are the problems in that it takes time until the pen tip is filled with the ink and that starving is slightly brought about.
In light of the problems on the conventional techniques described above, the present invention intends to solve them, and an object thereof is to provide a writing instrument having an excellent cap-off performance in which a pen tip is quickly filled with an ink and starving is not caused and which has a stable ink discharge amount and provides a good writing performance even after the pen tip is left to stand in the air over a long period of time.